The baboon serves as a model for endocrine events in human pregnancy. We examined normal baboon pregnancy for changes in serum testosterone (T), androstenedione (A) and dehydroepiandrostenedione (D). Blood samples were collected at 2-3 day intervals starting at 70 days of gestation. Pregnancies were terminated at 100 days (n=9) or 160 days (n=6) as part of another study and maternal, fetal, uterine and utero-ovarian vein samples were obtained. T, A and D were measured by direct RIA. Maternal serum levels of T between 70 and 160 days were generally at the lower limits of the assay (0.1 ng/ml). Levels of A increased with peak levels from 2-4 ng/ml, slightly less than human values, and showed a tight correlation with serum levels of D. Fetal serum levels of A and D were generally many times higher than the low levels in the maternal serum. The patterns and serum levels of these androgens are different from those in the human. T especially shows minimal levels in serum. Levels of A are alower than in the human but show a slight increase with advancing gestation.